Traefik Bad Gateway

Another reason can be that you might be accidentally mapping to the vm's port instead of the container port.

I made a change to my port mapping on the docker-compose file and forgot to update the labeled port so it was trying to map to a port on the machine that was not having any process attached to it

Wrong way:

ports:
  - "8080:8081"
labels:
  - "traefik.http.services.front-web.loadbalancer.server.port=8080"

Right way

ports:
  - "8080:8081"
labels:
  - "traefik.http.services.front-web.loadbalancer.server.port=8081"

Also in general don't do this, instead of exposing ports try docker networks they are much better and cleaner. I made my configuration documentation like a year ago and this was more of a beginner mistake on my side but might help someone :)

If you see Bad Gateway with Traefik chances are you have a Docker networking issue. First have a look at this issue and consider this solution. Then take a look at providers.docker.network (Traefik 2.0) or, in your case, the docker.network setting (Traefik 1.7).

You could add a default network here:

[docker]
endpoint = "unix:///var/run/docker.sock"
domain = "example.com"
watch = true
exposedbydefault = false
network = "proxy"

Or define/override it for a given service using the traefik.docker.network label.

For anyone getting the same issue:

After recreating the network (proxy) and restarting every site/container it seems to work now. I still don't know where the issue was from.

Got the same problem and none of the above mentioned answers solved it for me. In my case a wrong loadbalancer was added. Removing the label or changing it to the correct port made the trick.

 - "traefik.http.services.XXX.loadbalancer.server.port=XXX"